Process for the liquefaction and decomposition of air



Patented Jan. 7, 1941 UNITED STATES PATENT OFFICE PROCESS FOR THELIQUEFACTION AND DE- COMPOSITION OF AIR- NorDrawing. Application July29, 1939, Serial No. 287,409. In Germany August 17, 1938 8Claim8.

In the process for the liquefaction and decomposition or rectificationof air. difiiculties are encountered due to the presence of smallamounts of acetylene in the air.

It has been proposed to avoid the danger of explosions due to thepresence of acetylene in the air which is to be subjected toliquefaction and rectification by providing a long air intake pipe whichextends beyond the surroundings of the i 10 liquefying and rectifyingapparatus in order to insure a supply of pure air. It has also beenproposed to withdraw from the process liquid oxygen in which theacetylene has become concentrated and to dispose of this oxygenseparately and with special precautions so as to avoid the danger fromexplosions. These expedients, however, are not always successful inavoiding explosions. In the operation of the air liquefying andrectifying process for the recovery of crypton and xenon, which handleslarge amountspf air,

it has been. observed that even with concentrations of acetylene whichare much smaller than those encountered when the above expedients areemployed (e. g. 10-100 parts per million of acetylene in the liquidoxygen calculated in. parts by volume of the components in the gaseousstate) which concentrations generally have been regarded as beingharmless, explosions frequently occur. It has been found to be im- 0possible completely to avoid the presence of acetylene in the air by theexercise of care in the location of the air intake and it has been foundto be impossible to vaporize the liquid oxygen containing acetylenewithout danger o explosion. In accordance with the present inventiondifliculties due to the presence of acetylene are avoided by subjectingthe air to a special treatment preferably after leaving the compressorand 4 before entering the decomposing apparatus. The

treatment may be described generally asone capable of breaking downozone although it is not asserted that ozone is the cause of theexplosions. It may be that other unstable oxygen compounds are presentor that particles or entities of higher energy level are present orformed as a result of the physical operations to which the air issubjected. It is practically impossible to prove these p ssibilities dueto the fact that the substances in question are unstable and/or presentin such lytical methods at present available. The treatinent of the airby a method designed to break up ozone is therefore merely a rule ofoperation because it is not known whether ozone is present or whether itis broken up. It is only known that treatments adapted to break up ozoneif it is present are effective.

For example the air, after being compressed. 5 may be additionallyheated above the temperature produced by the compression or it may bePassed, preferably at the temperature produced by the compression, overcatalytic surfaces. One suitable treatment is to pass the air aftercompression and without cooling through a bed of hog iron ore such as isused for removing sulfur from coal distillation gases. The air may besubjected to a chemical treatment with a reducing agent adapted todestroy ozone. This may be done by injecting the reducing agent infinely divided state into the air or by passing the air through ascrubbing tower where it is contacted with a liquid having a reducingaction. In the latter case the scrubbing of the air may serve also tocool the air i. e. to remove the heat generated by the compression. 7

I claim:

1. In a. process involving the compression, cooling, liquefaction andrectification of air, the step which consists in subjecting the-air.prior to liquefaction thereof to atreatment for the destruction ofozone.

2. Process as defined in claim 1 in which the 30 air is treated for thedestruction of its ozone content following the compression thereof.

3. Process as defined in claim 1 in which the treatment of the airconsists in heating it to a temperature above that attained in thecompressing operation.

4. Process asdefined in claim 1 in which th treatment of the airconsists in contacting it with a solid catalyst.

5. Process as defined in claim 1 in which the 0 air after compressionand prior to cooling is passed in contact with bog iron ore.

6. Process as defined in claim 1 in which the air is contacted with areducing agent.

7. Process as defined in claim 1 in which the 5 air is contacted with ascrubbing liquid containing a reducing agent.

8. Process as defined in claim 1 in which the air after compression andprior to cooling is contacted with a scrubbing liquid containing a re-50 ducing agent whereby the air is cooled and stmultaneously freed ofozone.

FRANZ POLIIIZER.

